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Thread: Parallel or tapered throat in a 7mm-08

  1. #1

    Parallel or tapered throat in a 7mm-08

    Right, I've finally decided to build a new 7mm-08, to which end I've acquired a Sako 75 stainless actioned rifle to use as a donor.
    In the past when talking to various gunsmiths about chambering a new barrel, some have said that their preference was to use a reamer which gave a parallel lead to the throat, as opposed to a standard SAMI spec tapered one.
    From these conversations and what research I've managed to do, it appears that the advantage of a parallel lead into the throat is that the rifle is less fussy about bullets of differing weights, lengths and seating depth.
    To any of the members who have experience of this or have rifles chambered thus, what are their thoughts / experiences. Are there any disadvantages?
    My current 7mm-08 has a 21 1/2" barrel, is there an optimum length for efficiently timing 120gn and 140gn ballistic tips?
    Last edited by DCG; 15-04-2014 at 14:55.

  2. #2
    Quote Originally Posted by DCG View Post
    Right, I've finally decided to build a new 7mm-08, to which end I've acquired a Sako 75 stainless actioned rifle to use as a donor.
    In the past when talking to various gunsmiths about chambering a new barrel, some have said that their preference was to use a reamer which gave a parallel lead to the throat, as opposed to a standard SAMI spec tapered one.
    From these conversations and what research I've managed to do, it appears that the advantage of a tapered throat is that the rifle is less fussy about bullets of differing weights, lengths and seating depth.
    To any of the members who have experience of this or have rifles chambered thus, what are their thoughts / experiences. Are there any disadvantages?
    My current 7mm-08 has a 21 1/2" barrel, is there an optimum length for efficiently timing 120gn and 140gn ballistic tips?
    AFAIK ... every chamber has a tapered lede, or there's an abrupt juncture at some point. You've switched from tapered lede to tapered throat in the 3rd sentence so I'm confused .... obviously a parallel section in either gives more latitude with different bullet profiles & seating depths ......... if that's what you mean.

    TBH .......... I haven't a clue what you mean about efficiently timing different bullet weights in deciding the best barrel length, but I'll eagerly await the answer if there is one.

    Maybe you need to get out more ......
    If I'm going to be accused of it then it's just as well I did it.

  3. #3
    maybe he means freebore like wetherby used with it's overbore chamberings?

    or maybe he means the angle of the lead into the rifling?

    I agree it's a little confusing ?
    Right where's those stones , I'll start !

  4. #4
    DCG
    If you want a copy of the SAAMI 7-08 cartridge & chamber drawing send me a P.M. with an email address & I will email it to you.
    In response to your question I would advise sticking to the standard SAAMI dimensions which do indicate taper angles.

    Ian

  5. #5
    TBH my only experience is with a Sako 75 Stn/Syn in 7mm08 which shoots sub 1/2" groups with 100gn Sierra Varminter HP's, 120gn Nosler BT's and 140 gn Nosler BT's and 140gn Sierra SP's so I don't know about Sako's factory throating but I do establish the optimum seating depth for each bullet type that I load.

    I would have thought that twist rate is more important than barrel length for bullet weight but what do I know?
    Knowledge is knowing that a tomato is a fruit. Wisdom is not using it in a fruit salad.

    Amateurs practice until they get it right. Professionals practice until they never get it wrong.

  6. #6
    Hi,Sinistral, Tackb,
    I've edited the original post so that it reads better, sorry about that,
    As I understand it ( and I could have got this completely wrong) some gunsmiths specify their reamers with a parallel lead into the throat as opposed to a tapered lead, I guess this would then make the throat steeper possibly and or longer. The advantage, I was told, is that it makes the rifle more tolerant to variations in jump specifically and other factors.
    I don't think it alters the free bore, you would specify that, if you were that way inclined, depending on the model and desired seating depth of your chosen bullet.
    Perhaps if someone that does know what I'm on about sees this post, they would be kind enough to comment.
    If you don't ask you don't find out !
    dcg

  7. #7
    Hi Yorric
    Thanks for your reply and your kind offer, to be honest the dimensions don't really matter. Having been recommended to use this parallel lead, I was more interested to find out if it had any practical disadvantages,
    in my experience, if something appears to be to good to be true, it usually is

  8. #8
    Quote Originally Posted by DCG View Post
    Hi Yorric
    Thanks for your reply and your kind offer, to be honest the dimensions don't really matter. Having been recommended to use this parallel lead, I was more interested to find out if it had any practical disadvantages,
    in my experience, if something appears to be to good to be true, it usually is
    Phone a couple of guys that cut reamers and get their take on what works and what doesn't work would be my suggestion. Regards JCS

  9. #9
    Parallel lead sounds like "free-bore". I would get the standard SAAMI chamber... or what ever TIKKA uses on their rifles. Works for me....~Muir

  10. #10
    Quote Originally Posted by Muir View Post
    Parallel lead sounds like "free-bore". I would get the standard SAAMI chamber... or what ever TIKKA uses on their rifles. Works for me....~Muir
    Hi Muir,
    I was hoping that you'd see the thread and might have the definative answer.
    As I understand it so far( and I might have the terminology wrong and got hold of the wrong end of the stick, so I stand to be corrected), on a standard Sami spec chamber, the lead runs from the end of the neck starting about .005"over bore at aprox 45' of angle until lit hits the bore where it changes to to aprox 1.5 degrees as it cuts into the lands.
    What I have had described is that (I think) the leads runs from the end of the neck at about .005" overbore parallel until lit reaches a point were it intersects an angle of 1.5 degrees which is cut up to the bore continuing through the lands.
    i don't think that the lands in either case would be at a different point in relation to the end of the neck, therefore unless specified differently the freeborn will be more or less the same in either case.
    The advantages from a shooting point of view as described, seem to stack up. However I am sceptical that there must be a trade off. I can accept that from an engineering point of view, in the way that a chamber is reamed, it's more difficult to ream a parallel hole to exact tolerances,than a tapered one. But surely this can't be the only reason that it's not more common.

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